Microencapsulation is the envelopment of an active agent or a core material within a solid wall material. The active or core material can be in the form of a solid particle, a liquid droplet, or a gas bubble. The solid coating used to form the capsule may be, for example, an organic polymer, a wax, or an inorganic oxide.
Many consumer and industrial products employ microencapsulated products to enable effective delivery of active ingredients. For example, fragrances, oils, in-stable inorganic chemicals, agricultural active ingredients, and pharmaceutically active ingredients are commonly commercially deployed with microencapsulation technology. The background for this technology is outlined in “Microencapsulation,” Encyclopedia of Polymer Science and Technology, John Wiley and Sons, New York, 2005, the contents of which are hereby incorporated by reference. Examples of microencapsulated particles are presented in FIG. 1.
Several challenges exist for these products. First, encapsulated materials in formulated products should be stable to minimize leakage of the interior components through the shell-wall into the surrounding medium. Second, there should be compatibility and stability between the shell-wall and the surrounding media. Third, the physical strength of the shell-wall should be adjusted to enable the desired breakage behavior for controllable release of interior components. Fourth, the charge of the shell-wall should be adjusted to improve the microencapsulated particle's affinity to a desired surface(s).
In WO 2008/005693A2, A. Farooq et. al. describe the use of lactamic polymers, such as polyvinyl pyrrolidone (PVP), PVP/vinyl acetate (PVP/VA), and poly(vinyl pyrrolidone-co-dimethylaminoethyl methacrylate) (VP/DMAEMA), to treat the surface of microencapsulated particles to improve stability of microencapsulated fragrance particles in fabric softeners. The relevant disclosure in this publication is hereby incorporated by reference.
In U.S. Pat. No. 7,271,204 (B2), R. Fechter et al. describe a method for producing fragrant coating compositions employing UV curable monomers and oligomers. However, the resulting product is not in particulate, or microcapsule, form.
In U.S. Pat. No. 7,119,057 (B2), L. M. Popplewell et al. describe a method for producing fragrant microencapsulated particles that are subsequently coated with a cationic polymer. The initial microencapsulated particles are formed by dispersing poly(acrylamide-co-acrylic acid) and methylated melamine-formaldehyde resin in water followed by the addition of the desired fragrance. Adjustment of pH and elevated temperatures enable cross-linking of the dispersed fragrance droplets. These microencapsulated particles are then treated with a cationic polymer, such as cationic starch or guar.
In U.S. Pat. No. 4,608,330, C. P. Marabella describes a method for producing microcapsules comprised of photo-sensitive compounds. Among the components of the internal phase are trimethylolpropanetriacrylate and a photoinitiator (Irgacure 651). The internal phase is encapsulated by cross-linking isobutylene-maleic anhydride copolymer (Isobam-10) with a urea-formaldehyde resin.